There has been conventionally known a developer container having a container body formed with a toner filling port and a toner cap closing the toner filling port. One example of such a toner cap includes an insertion part and a flange part. The insertion part has a base end and a tip end opposite to the base end. The flange part extends radially outwardly from the base end of the insertion part. The insertion part is inserted into the toner filling port. The flange part is bonded to an external surface of the container body by welding.